*{padding:0;margin:0}
html,body {
    height: 100%;
    background-color: #000;
}
.fu {
    width: 200px;
    height: 30px;
    background-color: #fff;
    border: 3px solid #ccc;
    position: relative;
}
.fu .blood {
    height: 30px;
    background-color: red;
    position: absolute;
}